Some types of implantable medical devices are configured to administer electrical stimulation to certain target tissues. As an example, cardiac rhythm management devices can be configured to deliver electrical stimulation pulses to cardiac tissue. As another example, neurological stimulation devices can be configured to deliver electrical stimulation pulses to nervous tissue.
In many cases, the implantable electrical stimulation systems include what is commonly referred to as a pulse generator and leads. The pulse generator is usually a sealed case containing circuitry configured to generate electrical stimulation pulses. These pulses then pass through one or more conductors in the leads before being delivered to a specific target tissue through electrodes that interface with the target tissue.
Frequently, fixation elements are used in conjunction with leads. Fixation elements can aid in keeping an electrode properly engaged with a target tissue for delivery of electrical stimulation. Existing fixation systems can include both active and passive fixation elements. Active fixation elements usually have a component, such as a screw or hook, which is inserted into the target tissue, such as into the myocardium. However, insertion of an active fixation element can sometimes result in undesirable trauma to the target tissue. Passive fixation elements usually include appendages, such as tines, that are designed to lodge in tissue, such as in the trabeculae of the atrium or ventricle. The appendages, in conjunction with tissue that grows around the appendages, function to anchor the electrode in place. However, passive fixation elements are not always effective to secure a lead in place, because of lack of suitable trabeculae in a desired target area and vigorous cardiac wall movement.
In some cases, leads must be removed (explanted) after a period of time in the body of a patient. Reasons for explant procedures can include infection, lead malfunction, lead dislodgement, and the like. However, fibrous tissue sometimes grows around the lead after a period of time due to the human body's immunological response to a foreign body. This fibrous tissue can make it very difficult to remove the old leads, increasing the risks of complications during the explant procedure.
For at least these reasons, a need remains for implantable leads that can be fixed in place. A need also exists for implantable leads that can be explanted while reducing risks of complications.